Catadioptric projection objective with geometric beam splitting

ABSTRACT

A projection exposure lens has an object plane, optical elements for separating beams, a concave mirror, an image plane, a first lens system arranged between the object plane and the optical elements for separating beams, a second double pass lens system arranged between the optical elements for separating beams and the concave mirror, a third lens system arranged between the optical elements for separating beams and the image plane. The second lens system has a maximum of five lenses.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/282,587,filed Nov. 21, 2005, which is a Divisional of application Ser. No.10/734,623, filed Dec. 15, 2003, which is a Continuation-in-Part ofapplication Ser. No. 09/751,352, filed Dec. 27, 2000, which claims thebenefit of Provisional Application No. 60/173,523, filed Dec. 29, 1999,and of Provisional Application No. 60/222,798, filed Aug. 2, 2000; theContinuation-in-Part application Ser. No. 10/734,623 additionally claimsthe benefit of Provisional Application No. 60/511,673, filed Oct. 17,2003. The entire disclosures of the prior applications listed above areconsidered part of the disclosure of the present application and arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a catadioptric projection objective forprojecting a pattern arranged in an object plane of the projectionobjective into an image plane of the projection objective with theformation of at least one real intermediate image at an image-sidenumerical aperture NA>0.7.

2. Description of the Related Prior Art

Projection objectives of this type are used in microlithographyprojection exposure systems for producing semiconductor components andother finely structured components. They are used to project patterns ofphoto masks or engraved plates, which in the following text willgenerally be designated masks or reticles, onto an object coated with alight-sensitive layer, with extremely high resolution on a reducingscale.

In this case, in order to generate finer and finer structures, it isnecessary, firstly, to enlarge the image-side numerical aperture NA ofthe projection objective and, secondly, to use shorter and shorterwavelengths, preferably ultraviolet light with wavelengths of less thanabout 260 nm, for example 248 nm, 193 nm or 157 nm.

For wavelengths down to 193 nm, it is possible to operate with purelyrefractive (dioptric) projection systems, whose production can bemanaged easily because of their rotational symmetry about the opticalaxis. In order to achieve extremely small resolutions, however, it isnecessary here to operate with extremely large numerical apertures NA ofmore than 0.8 or 0.9. In the case of dry systems with an adequatelylarge, finite working distance (distance between the exit face of theobjective and the image plane), these can be implemented only withdifficulty. Refractive immersion systems have also already been proposedwhich, by using an immersion liquid of high refractive index betweenobjective exit and image plane, permit values of NA>1.

For the aforementioned short wavelengths, however, it becomes more andmore difficult to provide purely refractive systems with adequatecorrection of color errors (chromatic aberration), since the Abbéconstants of suitable transparent materials are relatively close to oneanother. Therefore, for extremely high resolution projection objectives,use is predominantly made of catadioptric systems, in which refractiveand reflective components, in particular therefore lenses and refractivemirrors, are combined.

When using projecting reflecting surfaces, it is necessary to use beamdeflection devices if obscuration-free and vignetting-free projection isto be obtained. Both systems with geometric beam splitting by means ofone or more wholly reflecting folding mirrors (deflection mirrors) andsystems with physical beam splitting are known. Furthermore, planarmirrors can be used for folding the beam path. These are generally usedin order to meet specific installation space requirements or in order toalign the object and image plane parallel to each other. These foldingmirrors are optically not absolutely necessary.

The use of a physical beam splitter, for example in the form of a beamsplitter cube (BSC), with polarization-selective beam splitter surfacemakes it possible to implement projection objectives with an objectfield centered on the optical axis (one-axis systems). The disadvantagewith such systems is that suitable transparent materials for theproduction of a beam splitter cube are available only to a limitedextent in the required large volumes. In addition, the production of thepolarization-selectively effective beam splitter layers presentsconsiderable difficulties. An incomplete polarization-selective actioncan lead to the production of leakage transmission dependent on theangle of incidence and therefore to intensity inhomogeneities in theprojection.

The disadvantage of systems with polarization-selective beam splitterscan largely be avoided in systems with geometric beam splitting, that isto say when wholly reflective folding mirrors are used in the beamdeflection device. Such a folding mirror permits the optical pathleading to a concave mirror to be separated physically from the opticalpath leading away from the concave mirror. Many problems which canresult from the use of polarised light are eliminated.

In the case of projection objectives with geometric beam splitting,various folding geometries are possible, there being specific advantagesand disadvantages, depending on the course of the light path betweenobject field and image field.

U.S. Pat. No. 6,195,213 B1 shows various embodiments of projectionobjectives with geometric beam splitting for projecting a pattern of amask arranged in an object plane of the projection objective into animage plane of the projection objective with the formation of a single,real intermediate image. The projection objectives, which reachimage-side numerical apertures up to NA=0.75, have a catadioptric firstobjective part, which is arranged between the object plane and the imageplane and has a concave mirror and a beam deflection device, and also adioptric second objective part, which is arranged between the firstobjective part and the object plane. The elements of the first objectivepart used for forming the intermediate image are designed in such a waythat the intermediate image lies optically and geometrically in thevicinity of the first folding mirror. The beam deflection device has afirst folding mirror, which is arranged in the beam path between theconcave mirror and the image plane. In these systems, the first foldingmirror is arranged in such a way that light coming from the object planefalls firstly on the concave mirror of the first objective part beforeit is reflected by the latter to the first folding mirror. From thelatter, it is deflected by 90° and reflected to a second folding mirror,which deflects the radiation coming from the first folding mirror oncemore through 90° in the direction of the image plane. This beam guidanceleads to an h-shaped structure of the system, for which reason thisfolding geometry is also designated h-folding. The projection objectivehas only one concave mirror.

Accommodated in the space between object plane and first folding mirrorare a plurality of lenses used for the optical correction. The regionbetween the folding mirrors is free of lenses, which is intended topermit a compact design. Therefore all the lenses and the concave mirrorare arranged in objective parts which can be aligned vertically, whichis intended to achieve a structure which is stable with respect to theinfluences of gravity.

In U.S. Pat. No. 5,969,882 (corresponding to EP-A-0 869 383), otherprojection objectives with h-folding and only one concave mirror aredescribed, in which lenses are arranged in the space between objectplane and first folding mirror. In embodiments in which the first andthe second folding mirror are configured as reflective surfaces of adeflection prism, the region between the folding mirrors is free of anyrefractive power.

European Patent EP 0 604 093 B1 and U.S. Pat. No. 5,668,673 connectedthereto via a common priority show catadioptric projection objectiveswith relatively low numerical apertures of NA<0.5, in which the objectfield is projected into the image field with the aid of two concavemirrors, forming a single real intermediate image. Embodiments withdifferent, partly complex folding geometries are shown, in someembodiments a first beam section running from the object plane to aconcave mirror and a second beam section running from this concavemirror to the image plane crossing. The complex folding geometries witha large number of optical components physically close to one anothermean that considerable mechanical and mounting problems may be expectedin the practical implementation of such designs. A transfer of thedesign concepts into the area of higher numerical apertures appears notto be practical, on account of the associated greater maximum beamdiameters and the correspondingly increasing maximum lens diameters.

European Patent EP 0 989 434 (corresponding to U.S. Pat. No. 6,496,306)shows projection objectives with a beam deflection device formed as amirror prism. The mirror prism forms the first folding mirror for thedeflection of the radiation coming from the object plane to the concavemirror, and a second folding mirror for the deflection of the radiationreflected from the concave mirror to the second objective part, whichcontains only refractive elements. The catadioptric first objective partforms a real intermediate image, which is located freely accessibly at adistance behind the second reflecting surface. The single concave mirroris fitted in a side arm of the projection objective which projectstransversely with respect to the vertical direction when installed andwhich is also designated a “horizontal arm” (HOA). On account of the1-form geometry of the beam path, such a folding geometry is alsodesignated “1-folding”. Other projection objectives with only oneconcave mirror and 1-folding are described, for example, in DE 101 27227 (corresponding to US Patent Application US 2003/021040) or theInternational Patent Application WO 03/050587.

Systems with geometric beam splitters have the disadvantage, caused bythe principle, that the object field is arranged eccentrically withrespect to the optical axis (extra-axial system or off-axis system).This places high requirements on the correction of image errors since,in such a projection system, as compared with on-axis systems, a largerusable field diameter has to be corrected adequately with the sameobject field size. This larger field area, including the object field,will also be designated the “superfield” in the following text.

Optimization of the size of the superfield becomes more and moredifficult as the numerical aperture of the projection objectiveincreases, since the clearances for the arrangement and dimensioning ofoptical components and here, in particular, the folding mirror, becomesmaller and smaller, with the limiting condition of vignetting-freeprojection. In addition, the mechanical mounting of the opticalcomponents increasingly presents difficulties the more complex theirrelative arrangement to one another is.

SUMMARY OF THE INVENTION

It is an object of the invention to provide catadioptric projectionobjectives which, with a finite working distance, permit a higherprojection quality, even at extremely high numerical apertures. In thiscase, a beneficial geometry for stable mounting of optical components isto be achieved. In particular, an increase in the image-side numericalaperture in regions of NA≧0.8 or NA≧0.9 is to be made possible which,when such projection objectives are used in immersion lithography or innear field lithography, permit usable numerical apertures of NA≧1.

As an achievement of this object, according to one formulation of theinvention, the invention provides a catadioptric projection objectivefor projecting a pattern arranged in an object plane of the projectionobjective into an image plane of the projection objective, in which atleast one real intermediate image is formed during the projection and animage-side numerical aperture of NA>0.7 is achieved. The projectionobjective comprises:

an optical axis; andat least one catadioptric objective part that comprises a concave mirrorand a first folding mirror;wherein a first beam section running from the object plane to theconcave mirror and a second beam section running from the concave mirrorto the image plane can be generated;and the first folding mirror is arranged with reference to the concavemirror in such a way that one of the beam sections is folded at thefirst folding mirror and the other beam section passes the first foldingmirror without vignetting, and the first beam section and the secondbeam section cross one another in a cross-over region.

The crossed beam guidance in the region of the catadioptric objectivepart permits projection objectives with a compact and mechanicallystable arrangement of the optical components. In this case,vignetting-free beam guidance can be achieved, so that no folding mirrorcuts a beam which is reflected either at the folding mirror or is ledpast the folding mirror without reflection. In this way, only the systemaperture stop limits, in an axially symmetrical way, the angulardistribution of the beams which contribute to the imaging. At the sametime, even at extremely high numerical apertures, which are associatedwith large maximum beam diameters and possibly highly convergent ordivergent beams in the region of field planes, a moderate size of thesuperfield to be corrected can be achieved.

The invention can be used in different folding geometries. In someembodiments, the first folding mirror is arranged such that the firstbeam section is folded at the first folding mirror and the second beamsection passes the first folding mirror without vignetting. In thiscase, the first folding mirror typically has a reflecting surface facingaway from the optical axis. This beam guidance, in which the radiationrunning indirectly or directly from the object plane to the catadioptricobjective part strikes the first folding mirror first, is typical ofobjectives with the 1-folding mentioned at the beginning.

In other embodiments, the first folding mirror is arranged such that thefirst beam section, that is to say the radiation coming directly orindirectly from the object plane, passes the first folding mirrorwithout vignetting and the second beam section, that is to say theradiation reflected by the concave mirror, is folded at the firstfolding mirror. Here, the first folding mirror can have a reflectingsurface facing the optical axis, so that the radiation on the path fromthe concave mirror to objective parts arranged downstream and to theimage plane crosses the optical axis and the first beam section. Thisbeam guidance is typical of the h-designs mentioned at the beginning.

In many advantageous embodiments, the projection objective has only asingle concave mirror. However, embodiments with more than one concavemirror are also possible. Such embodiments can contain a plurality ofcatadioptric objective parts, of which one or more can have the crossedbeam guidance.

It may be beneficial if the projection objective has at least one secondfolding mirror in addition to the first folding mirror. Additionalfolding mirrors can be used for the purpose of aligning object plane andimage plane parallel to each other. Additional folding mirrors are alsorequired when further catadioptric objective parts with geometric beamsplitting are provided. Within the scope of the invention, there areembodiments with one or more catadioptric objective parts.

The first and the second folding mirrors can be fitted to a commoncarrier. The first and the second folding mirrors are preferablyseparate folding mirrors, which are mounted in separate mounts and, ifappropriate, can be set or adjusted separately from one another. Thefolding mirrors can be fitted on different sides of the optical axis.The folding mirrors can be fixed stably on mutually opposite sides ofthe mount construction of the projection objective with the aid ofcompact fixing constructions. A separate mounting of the folding mirrorscan also be advantageous with regard to the fact that, as a rule, onlyone of the mirror edges is critical with regard to the vignetting of thebeam. These can be positioned beneficially given separate mounting offolding mirrors.

Projection objectives according to the invention can have one or morereal intermediate images. In the region of an intermediate image thereexists a local minimum of the beam diameter, so that it is generallybeneficial to fit a folding mirror geometrically and/or optically in thevicinity of an intermediate image. In one embodiment, the first foldingmirror has an inner mirror edge near the optical axis and anintermediate image is arranged in the geometric vicinity of the innermirror edge. The intermediate image can be the single intermediate imageof the projection objective, which preferably has a beam foldinggeometry typical of 1-folding. The geometric distance between theintermediate image and the inner mirror edge is preferably less than 30%or less than 20% or less than 10% of the meridional extent of theintermediate image.

In some embodiments, in particular in embodiments with 1-folding, thefirst folding mirror has an inner mirror edge near the optical axis, andan intermediate image is arranged in a geometric space between the innermirror edge and the object plane. In these embodiments, it is possiblefor the beam to be “forced through” between the first folding mirror andthe field plane placed geometrically upstream of the latter and/or anoptical component placed geometrically upstream of the folding mirrorwithout vignetting.

In some embodiments, the upstream field plane is the object plane. Inother embodiments, one or more refractive and/or catadioptric projectionsystems can be connected upstream of the catadioptric objective partwhich has the crossed beam guidance, so that the upstream field plane isan intermediate image plane of the projection objective.

It can be beneficial if the at least one intermediate image is arrangedin the optical vicinity of a folding mirror. An optical vicinity of afolding mirror is characterized in particular by the fact that neitherlens nor any other optical element is arranged between the intermediateimage and the most closely situated folding mirror. Sometimes, anintermediate image is arranged in the optical vicinity of a secondfolding mirror, not necessary for the beam separation. An arrangement ofan intermediate image such that at least part of the intermediate imagefalls on a reflecting surface of a folding mirror should be avoided, onthe other hand, since this can lead to errors which may be present inthe reflecting surface being projected sharply into the image plane. Aspacing between intermediate image and reflecting surface is thereforeadvantageous.

One class of projection objectives according to the invention has only asingle real intermediate image as well as a single concave mirror andtwo folding mirrors, which are aligned for parallel alignment of objectplane and image plane. In this case, both h-folding and 1-folding arepossible.

Other embodiments have two or more real intermediate images, inparticular at least three real intermediate images. Embodiments havingat least three real intermediate images have a first objective part forprojecting the object field into a first real intermediate image, asecond objective part for forming a second real intermediate image withthe radiation coming from the first objective part, a third objectivepart for forming a third real intermediate image from the radiationcoming from the second objective part, and a fourth objective part forprojecting the third real intermediate image into the image plane.

In preferred systems, the third intermediate image is projected into theimage plane directly, that is to say without the formation of furtherintermediate images, so that there are precisely three real intermediateimages.

The first objective part can serve as a relay system, in order to form afirst intermediate image with a predefinable correction state at asuitable position from the radiation coming from the object plane.

At least two of the objective parts are preferably catadioptric and ineach case have a concave mirror. In particular, precisely twocatadioptric objective parts can be provided.

In one development, the second objective part and the third objectivepart are constructed with one concave mirror in each case. Each of theconcave mirrors is assigned a folding mirror, in order either to deflectthe radiation to the concave mirror or to deflect the radiation comingfrom the concave mirror in the direction of a following objective part.

The fourth objective part is preferably purely refractive and can beoptimized in order to produce high image-side numerical apertures (NA).

Preferred embodiments comprise four objective parts, which are groupedin a cross-like arrangement wherein, at one or more points of thecomplexly folded beam path, cross-over regions can arise in which thefirst beam section running from the object plane to a concave mirror andthe second beam section running from the concave mirror to the imageplane cross one another.

The provision of at least two catadioptric subsystems has greatadvantages. In order to see substantial disadvantages of systems withonly one catadioptric subsystem, it is necessary to consider how, in acatadioptric objective part, the correction of the Petzval sum and ofthe chromatic aberrations is carried out. The contribution of a lens tothe longitudinal chromatic aberration CHL is given by

CHL∝h²·φ·ν

that is to say it is proportional to the marginal beam height h (as thesquare), the refractive power φ of the lens and the dispersion ν of thematerial. On the other hand, the contribution of a surface to thePetzval sum depends only on the surface curvature and the refractiveindex step (which is −2 in the case of a mirror).

In order to allow the contribution of the catadioptric group to thechromatic correction to become large, large marginal beam heights aretherefore needed (that is to say large diameters); in order to allow thecontribution to the Petzval correction to become large, large curvatures(that is to say small radii, which are most expediently achieved withsmall diameters). These two requirements oppose each other.

The opposing requirements for Petzval correction (that is to saycorrection to the curvature of the image field) and chromatic correctioncan be solved by the introduction of (at least) a further catadioptricpart into the system.

The two catadioptric systems can be designed asymmetrically in such away that one has a trend to a large diameter with flat radii for CHLcorrection and the other has a trend to a small diameter with curvedradii for Petzval correction. A symmetrical structure is likewisepossible and can be beneficial from the point of view of simplefabrication.

In general, the degree of freedom consists in distributing thecorrection of these and other image errors uniformly or nonuniformly totwo (or more) catadioptric subsystems. In this way, with a structure onwhich the requirements are relaxed, extremely high apertures with anexcellent state of correction can be implemented.

The invention makes it possible to provide catadioptric projectionobjectives in which, even at extremely high numerical apertures, thegeometric optical conductance to be corrected does not become too high.The geometric optical conductance (or etendue) is defined here as theproduct of the image-side numerical aperture and the field size. In someembodiments, a diagonal ratio between the length of the diagonal of aminimum circle centered on the optical axis and enclosing the objectfield (superfield diagonal) and the length of a diagonal of the objectfield is less than 1.5, in particular less than 1.4 or less than 1.3 orless than 1.2.

The invention makes it possible to provide easily correctablecatadioptric projection objectives which, with a compact design andmechanically stable structure, can achieve extremely high numericalapertures. There are embodiments which are designed as “dry objectives”.Dry objectives are distinguished by the fact that they are designed forthe purpose in which, between the exit side of the projection objectiveand an input coupling surface of an object to be exposed, for example awafer, there is in operation a gap which is filled with gas and whosegap width is typically considerably larger than the working wavelength.In such systems, the numerical apertures that can be achieved arerestricted to values NA<1 since, as the value NA=1 is approached, totalreflection conditions occur at the exit face, which prevent illuminatinglight being coupled out of the exit face. The image-side numericalaperture in preferred embodiments of dry systems is NA>0.8, even NA>0.85or NA>0.9 being possible.

Within the scope of the invention, catadioptric projection objectiveswhich are designed as immersion objectives are also possible. In thecase of immersion lithography, as is known, the achievable resolution ofan exposure process is improved by the fact that an immersion mediumwith high refractive index is introduced into the space between the lastoptical element of the projection objective and the substrate, forexample an immersion liquid which has a refractive index n_(I)≧1.3 atthe working wavelength. As a result, projection objectives orprojections with an image-side numerical aperture NA>1.0 are possible,preferably NA≧1.1 or NA≧1.2 or NA≧1.3 being possible.

The optical structure also permits use for non-contact near-fieldprojection lithography. In this case, coupling of sufficient lightenergy into the substrate to be exposed via a gap filled with the gas ispossible if a sufficiently low image-side working distance is maintainedon average over time. This distance should lie below four times theworking wavelength used, in particular below the working wavelength. Itis particularly beneficial if the working distance is less than half theworking wavelength, preferably less than one third, one quarter or onefifth of the working wavelength. At these short working distances,projection in the optical near field can be carried out, in whichevanescent fields, which exist in the immediate facility of the lastoptical face of the projection system, are used for the projection.

The invention therefore also comprises a non-contact projection exposuremethod in which evanescent fields of the exposure light, which are foundin the immediate vicinity of the exit face, are made useful to thelithographic process. In this case, at sufficiently low (finite) workingdistances, in spite of geometric total reflection conditions at the lastoptical face of the projection objective, a proportion of light that canbe used for lithography is coupled out of the exit face of the objectiveand coupled into an input coupling surface immediately adjacent at adistance.

Embodiments for non-contact near field projection lithography havepreferably typical working distances in the range of the workingwavelength or less, for example between about 3 nm and about 200 nm, inparticular between about 5 nm and about 100 μm. The working distanceshould be matched to the other properties of the projection system(properties of the projection objective close to the exit face,properties of the substrate close to the input coupling surface) suchthat, on average over time, an input coupling efficiency of at least 10%is achieved.

Within the scope of the invention, a method for producing semiconductorcomponents and the like is thus possible, in which a finite workingdistance between an exit face for exposure light assigned to theprojection objective and an input coupling surface for exposure lightassigned to the substrate is set, the working distance being set withinan exposure time interval at least temporarily to a value which issmaller than a maximum extent of an optical near field of the lightemerging from the exit face.

The above and further features also emerge from the description and fromthe drawings, as well as from the claims, it being possible for theindividual features, in each case on their own or in a plurality, to beimplemented in the form of sub-combinations in an embodiment of theinvention and in other fields and for them to represent embodiments thatare advantageous and intrinsically capable of protection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a projection exposure systemfor immersion lithography with an embodiment of a catadioptricprojection objective according to the invention;

FIG. 2 is a lens section through a first embodiment of a catadioptricimmersion objective according to the invention with geometric beamsplitter and 1-folding;

FIG. 3 is a schematic diagram which shows a rectangular object fieldarranged eccentrically in relation to the optical axis and a circularsuperfield to be corrected;

FIG. 4 shows the projection objective shown in FIG. 2 in an illustrationsuitable for comparison with FIG. 5;

FIG. 5 shows a catadioptric projection objective with the same opticalstructure as in FIG. 4 but with a conventional geometric beam splitter;

FIG. 6 shows a further embodiment of a catadioptric projection objectivewith a geometric beam splitter and 1-folding, which is designed fornon-contact near field lithography;

FIG. 7 shows a detailed view of the region of folding mirrors of anotherembodiment of a catadioptric projection objective according to theinvention with geometric beam splitting;

FIG. 8 shows an embodiment of a catadioptric dry objective withgeometric beam splitting and h-folding according to an embodiment of theinvention;

FIG. 9 a shows an embodiment of an immersion projection objectiveaccording to the invention having two intermediate images with a crossshape and asymmetrical structure of two catadioptric objective parts;

FIG. 9 b shows a detailed view of the folding device in FIG. 8;

FIG. 10 shows a variant of the system shown in FIG. 9 a with obliquehorizontal arms;

FIG. 11 shows an embodiment of a dry system according to the inventionhaving three intermediate images and a cross shape;

FIG. 12 shows a folding device with prism;

FIG. 13 shows another embodiment of a projection objective built up in across shape with a largely symmetrical structure;

FIG. 14 shows a further embodiment of a projection objective accordingto the invention with a relay system arranged between two catadioptricobjective parts;

FIG. 15 shows an embodiment of a projection objective according to theinvention with decoupled optical axes of the catadioptric objectiveparts;

FIG. 16 shows a further embodiment of a projection objective accordingto the invention with decoupled optical axes of the catadioptricobjective parts.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description of preferred embodiments, the term “opticalaxis” designates a straight line or a series of straight line sectionsthrough the centers of curvature of the optical components. The opticalaxis is folded at folding mirrors (deflection mirrors) or otherreflective surfaces. Directions and distances will be described as“image-side” if they are oriented in the direction of the image plane orof the substrate to be exposed and located there, and as “object-side”if they are oriented toward the object plane or a reticle located therewith reference to the optical axis. In the examples, the object is amask (reticle) having a pattern of an integrated circuit, it can also beanother pattern, for example a grating. In the examples, the image isprojected onto a wafer provided with a photoresist layer which acts as asubstrate; other substrates, for example elements for liquid crystaldisplays or substrates for optical gratings, are also possible.

In FIG. 1, a micro lithographic projection exposure machine in the formof a wafer stepper 1, which is provided for the production of highlyintegrated semiconductor components by means of immersion lithography,is shown schematically. The projection exposure machine 1 comprises, aslight source, an excimer laser 2 having a working wavelength of 193 nm,other working wavelengths, for example 157 nm or 248 nm, also beingpossible. An illumination system 3 connected downstream produces in itsexit plane 4 a large, sharply delimited, very homogeneously illuminatedillumination field matched to the telecentering requirements of theprojection objective 5 connected downstream. The illumination system 3has devices for selecting the illuminating mode and, in the example, canbe switched over between conventional illumination at a variable levelof coherence, annular field illumination and dipole or quadrupoleillumination.

Arranged behind the illumination system is a device 40 (reticle stage)for holding and manipulating a mask 6 such that the latter lies in theobject plane 4 of the projection objective 5 and can be moved in thisplane in a removal direction 7 (y direction) for scanning operation.

Behind the plane 4, also designated the mask plane, there follows thecatadioptric reduction objective 5, which projects an image of the maskwith a reduced scale of 4:1 onto a wafer 10 covered with a photoresistlayer. Other reduction scales, for example 5:1 or 10:1 or 100:1 or lessare likewise possible. The wafer 10 serving as light-sensitive substrateis arranged such that the flat substrate surface 11 with the photoresistlayer substantially coincides with the image plane 12 of the projectionobjective 5. The wafer is held by a device 50 (wafer stage), whichcomprises a scanner drive in order to move the wafer synchronously withthe mask 6 and parallel to the latter. The device 50 also comprisesmanipulators in order to move the wafer both in the z direction parallelto the optical axis 13 of the projection objective and in the x and ydirection at right angles to this axis. A tilting device having at leastone tilt axis running at right angles to the optical axis 13 isintegrated.

The device 50 provided for holding the wafer 10 is constructed for usein immersion lithography. It comprises a holding device 15 which can bemoved by a scanner drive and whose base has a flat recess to hold thewafer 10. By means of a circumferential edge 16, a flat liquid-tightholder that is open at the top is formed for a liquid immersion medium20, which can be introduced into the holder by devices not shown and canbe led away from said holder. The height of the edge is dimensioned suchthat the immersion medium put in can cover the surface 11 of the wafer10 completely and, when the working distance between the objective exitand wafer surface is set correctly, the exit-side end region of theprojection objective 5 can dip into the immersion liquid.

FIG. 2 shows the first embodiment of a catadioptric reduction objective100 designed for immersion lithography and having geometric beamsplitting. It is used to project a pattern of a reticle or the likearranged in its object plane 101 into an image plane 103 alignedparallel to the object plane on a reduced scale, for example in theratio 4:1, with the formation of a single real intermediate image 102.Between the object plane 101 and the image plane 103, the objective hasa catadioptric objective part 104, which comprises a concave mirror 105and a first, flat folding mirror 106, and also a purely refractivedioptric objective part 107 following behind the catadioptric objectivepart in the light path. Between the intermediate image 102 and the firstlens of the refractive objective part 107 there is arranged a secondfolding mirror 108, whose reflecting surface lies in a plane which isaligned at right angles to the plane of the reflective surface of thefolding mirror 106. The first folding mirror 106 has a reflectingsurface which predominantly faces away from the optical axis 110 andwhich is used to deflect the radiation coming from the object plane inthe direction of the concave mirror 105. The second folding mirror 108,which is situated geometrically closer to the object plane 101 than thefirst folding mirror 106, is arranged and aligned such that it deflectsthe radiation coming from the concave mirror in the direction of theimage plane 103. While the first folding mirror 106 is necessary for thebeam deflection toward the concave mirror 105, the second folding mirror108 can also be omitted. Then, without further deflection mirrors, theobject plane and the image plane would be substantially at right anglesto each other.

The first folding mirror 106 is inclined with respect to the opticalaxis 110 at an angle of inclination of about 40°, so that the side arm(horizontal arm, HOA) of the projection objective, bearing the concavemirror 105, is inclined at about 100° with respect to the parts of theoptical axis that are at right angles to the object and image plane.This ensures that the region of the concave mirror does not project intothe region of the devices provided to hold the reticle.

A first beam section 120 leads from the object plane 101 to the concavemirror 105 and is folded at the first folding mirror 106. A second beamsection 130 leads from the concave mirror 105 to the image plane 103 andis folded at the second folding mirror 108. The intermediate image 102is located in the immediate vicinity of the inner mirror edge 115, closeto the optical axis 110 and facing the object plane 101, of the firstfolding mirror in the space between the inner mirror edge 115 and thereticle plane, beneficially in such a way that the beam of the secondbeam section, converging toward the intermediate image 102 and divergingagain behind the latter, can pass through the first folding mirrorwithout being cut. As can be seen from FIG. 2, in this case the minimumgeometric distance between the inner mirror edge 115 and the beam in theregion of the intermediate image is considerably smaller than thediameter of the intermediate image lying in the section plane of theillustration and is less than about 20% of this diameter. Since theprojection scale of the first projection system comprising thecatadioptric objective part, which forms the intermediate image, isclose to β=1, this diameter corresponds substantially to the width ofthe object field in the removal direction or scanning direction 7 (ydirection). From an optical point of view, the intermediate image 102lies in the immediate vicinity of the second folding mirror 108, no lensbeing arranged between the intermediate image and the second foldingmirror.

The projection objective 100 represents an advantageous variant of the1-folding explained at the beginning, in which the intermediate imagelies geometrically between the object plane or the reticle and the firstfolding mirror 106 and the beam deflection is carried out with the aidof two separate mirrors. Further below, it will be explained in moredetail how, as a result of this unusual folding arrangement, the opticalconductance to be corrected or the superfield size of the entire systemcan be kept small, even in the case of extremely high numericalapertures.

During operation of the projection system, the light from theillumination system enters the projection objective on the side of theobject plane 101 facing away from the image and passes first of allthrough the mask arranged in the object plane. The transmitted lightthen passes through a plane-parallel entry plate 151 and a positivemeniscus lens 152 with a concave surface on the image side, designed asa half-lens, arranged between said entry plate and the first foldingmirror. Following deflection at the first folding mirror 106, a positivemeniscus lens 153 arranged between folding mirror and concave mirror inthe vicinity of the first folding mirror and having a spherical, concaveentry face which is opposite the folding mirror and an aspherical exitface, is passed through before a mirror group 175 is reached. The mirrorgroup 175 comprises two negative meniscus lenses 154, 155 which areplaced immediately before the concave mirror 105 and whose convex orelevated surface in each case points toward the concave mirror 105, andthe concave mirror 105 itself. The light reflected from a concave mirror105 and led back through the lenses 155, 154 and 153, which are passedtwice, then forms the real intermediate image 102 in the immediatevicinity of the mirror edge 115, facing the object, of the first foldingmirror.

The lenses of the refractive objective part 107 can be subdividedfunctionally into a transfer group T and a focusing group F and are usedjointly to project the intermediate image produced immediately in frontof the second folding mirror 108 into the image plane 103 on a reducedscale. The transfer group comprises three biconvex positive lenses 156to 158 following one another directly and a following negative meniscuslens 159 with an object-side concave face.

The focusing group, following at a distance, opens with a biconcavenegative lens 160 with a highly negative refractive power, which effectsa high amount of beam widening and, because of the high angle ofincidence of the radiation on its exit side, contributes effectively tothe correction of image errors. The three following positive lenses 161,162, 163 having aspherical entry faces and spherical exit faces initiatethe beam convergence. In the region of the system aperture stop 180there is situated a negative meniscus 164 with an image-side concaveface. This is followed by only positive lenses 165 to 169, which aresubstantially used to produce the high image-side numerical aperture.The last optical element before the image plane 103 is formed by aplane-convex lens 169, whose flat exit side is situated at a workingdistance of 2 mm in front of the image plane 103. In operation, thenarrow opening is filled with an immersion medium 190. In the example,extremely pure water with a reflective index n_(I)=1.437 (193 nm) isused as immersion liquid.

The specification of the design is summarized in table 1 in tabularform. In this case, column 1 specifies the number of the refractive,reflective or otherwise distinguished face, column 2 the radius r of theface (in mm), column 3 the distance d, designated the thickness, fromthe face to the following face (in mm), column 4 the material of acomponent and column 5 the refractive index of the material of thecomponent which follows the specified entry face. Column 6 shows themaximum usable half-diameter in mm. The overall length L of theobjective between object and image plane is about 930 mm.

In the embodiment, nine of the faces, namely the faces 5, 8=19, 10=17,12=14, 27, 33, 35, 37 and 47 are aspherical. Table 2 specifies thecorresponding asphere data, the heights of the meniscuses of theaspherical faces being calculated in accordance with the following rule:

p(h)=[((1/r)h ²)/(1+SQRT(1−(1+K)(1/r)²h²)]+C1*h ⁴ +C2*h ⁶+ . . .

Here, the reciprocal (1/r) specifies the radius of curvature of the faceat the vertex of the face, and h the distance of a point on the facefrom the optical axis. Thus, p(h) specifies this meniscus height, thatis to say the distance of the point of the face from the vertex of theface in the z direction, that is to say in the direction of the opticalaxis. The constants K, C1, C2, . . . are reproduced in table 2.

The immersion system 100 is designed for a working wavelength of about193 nm, at which the synthetic quartz glass (SiO₂) used for all thelenses has a refractive index n=1.5602. It is matched to extremely purewater as immersion medium (n=1.4367 at 193 μm) and has an image-sideworking distance of 2 mm. The image-side numerical aperture NA is 1.1,the projection scale is 4:1. The system is designed for an image fieldwith a size of 26×5.5 mm² and is doubly telecentric. The diagonal ratiobetween the length of a diagonal of a minimum circle centered on theoptical axis and enclosing the object field and the length of a diagonalof the object field (cf. FIG. 3) is about 1.26.

Some special features of the projection objective will be explained inmore detail by using FIGS. 3 to 5. In this case, FIG. 3 shows aschematic representation of the dimensioning of object field andsuperfield in the object plane of the projection objective, FIG. 4 afolding geometry in the case of a projection objective according to theinvention with a geometric beam splitter and 1-folding (cf. FIG. 2), andFIG. 5 a schematic representation of the beam course and the foldinggeometry in the case of a similar projection objective without a crossedbeam path.

On account of the geometric beam splitting, the projection objective hasan extra-axially arranged object field 200, there being a finite objectfield distance h between the optical axis 210 and the object field. Theobject field of the wafer scanner is rectangular or slot-like with ahigh aspect ratio and is identified by the length of its diagonal 201(slot diagonal). In order to be able to project this extra-axial objectfield with little aberration, it is necessary to correct the projectionobjective for a field size which is considerably larger than the objectfield itself. This circular superfield 202 which is enclosed by aminimum circle about the eccentric object field centered around theoptical axis 210, can be defined by the length of its diagonal 203,which is designated the superfield diagonal here. It can be seen bythose skilled in the art that the diagonal ratio between the length ofthe superfield diagonal and the length of the slot diagonal should lieas close as possible to 1 in order to have the lowest possible effort oncorrection in the case of an extra-axial object field.

By using FIGS. 4 and 5, the problem in minimizing the opticalconductance and the superfield diameter and the problem of adequatespace in the vicinity of the folding mirror will be explained by meansof a comparison between conventional 1-folding with two folding mirrorsfitted to a mirror prism (FIG. 5) and an embodiment according to theinvention with separate folding mirrors (FIG. 4). In this case, FIG. 4corresponds to the objective structure shown in FIG. 2. In both thefolding variants illustrated, the field size is 26·5.5 mm². The samedesign is used as a basis (cf. table 1), that is to say the same objectfield radius is corrected. Thus, in both folding variants, the distanceh of the object field from the optical axis (object field distance) isof the same size.

As a mechanical criterion for a comparison of the two folding variants,let it be assumed that the smallest distance of the edge of a lens fromthe object plane or reticle plane is to be sufficiently large in orderto avoid any detrimental effect on the construction of the reticlestage. Both folding systems are conceived in such a way that this isprovided in virtually the same way.

It can be seen that, in the variant shown in FIG. 4 with crossed beamguidance, the constructional-mechanical boundary condition can be met.For this purpose, it is merely necessary to design the first lens 152following the object plane as a cut-off lens, in order that the secondfolding mirror 108 does not collide with this lens or its mount. This isshown in FIG. 2. It can be seen that no beam cutting or vignettingoccurs at the folding mirrors 106, 108. In particular, the face of thefirst folding mirror 106 is sufficiently large that all of the radiationcoming from the object can be deflected toward the concave mirror andthe reflecting surface of the second folding mirror is sufficient todeflect the entire beam coming from the intermediate image in thedirection of the image plane. The beam is not cut by the partsprojecting into the beam path either, which contributes in particular tothe fact that the region of minimum beam diameter in the vicinity of theintermediate image 102 can be forced through at a distance between themirror edge closest to the reticle and the reticle.

In the case of conventional folding (FIG. 5), on the other hand, forvignetting-free deflection at the first folding mirror, it would benecessary for the latter to pass through the first lens 152′. This canbe attributed, inter alia, to the fact that the first folding mirror 106closest to the object plane is located on the same side as theextra-axial object field. This is precisely the opposite in the case ofthe folding according to FIG. 4, in which the folding mirror nearest tothe object (the second folding mirror 108) is located on the side of theoptical axis which is opposite the object field. It can further be seenin FIG. 5 that the light beams intersect in the vicinity of the tip ofthe prism which is formed by the mirror edges close to the axis andbelonging to the first and second folding mirrors. This would also leadto vignetting and therefore cannot be implemented.

In order to eliminate the first conflict, it will be necessary for thefirst folding mirror 106 to be fitted further away from the reticle.However, this would enlarge the folding mirror, as a result of which thesecond conflict in the vicinity of the prism edge of the folding prismwould become even more critical. As a consequence, the object field mustbe fitted further extra-axially and therefore (given an unchanged sizeof the superfield) can no longer have the full field size of 5.5 mm². Itcan be shown that, given the folding geometry shown in FIG. 5, only afield of a size of 16 5.5 mm² could be projected without vignetting,given the same corrected object field radius (that is to say given thesame superfield size). Here, a great advantage of the beam guidanceaccording to the invention is shown.

A further embodiment of a catadioptric projection objective 500 with ageometric beam splitting, a single concave mirror and a crossed beampath in 1-folding geometry will be shown using FIG. 6. The basicstructure is comparable with the embodiment of the projection objective100 according to FIG. 2, for which reason the same designations,increased by 400, will be used for the corresponding features. Thespecification of the design emerges from tables 3 and 4.

As distinct from the embodiment according to FIG. 2, an aspheric lenswith substantially no refractive power is arranged between the objectplane 501 and the first folding mirror 506. The entry to the objectiveis formed by a plane-parallel plate 551 and the low refractive powerasphere 551′ following the latter. In the beam path, which is passedthrough twice, between the first folding mirror 506 and concave mirror505, the positive refractive power in the vicinity of the intermediateimage 502 is provided by two positive lenses 553, 553′ which arearranged at a distance from each other and which jointly, with twonegative meniscus lenses 554, 555 arranged in front of the concavemirror, contribute to positioning the intermediate image 502 between themirror edge 515, facing the object, of the first folding mirror and theobject plane. Optically immediately behind the intermediate image, thesecond folding mirror 508 is located, which can be small on account ofthe proximity to the intermediate image and can therefore be movedcloser to the object plane. The function of the transfer group T isfulfilled by a single positive lens 556. The focusing group F has, infront of the system aperture stop 580, a positive meniscus 560 and anegative meniscus 561 (in each case with an image-side concave face), abiconvex positive lens 562 and an object-side concave meniscus 563 witha low refractive power immediately in front of the system aperture stop.Arranged between the latter and the image plane 503 are only positivelenses 564 to 567, the last of which is a planoconvex lens with a flatexit side. The image-side working distance between the flat exit faceand the image plane is set to the value 0. In this design, theprojection objective can be used for contact projection lithography bymeans of “solid immersion”. With slight modifications, it can be changedinto an immersion system with a finite working distance, whose regionwould have to be filled with an immersion medium. If the workingdistance is set, for example, to less than 100 nm and therefore only afraction of the working wavelength, then this projection system can beadapted to a use in near field lithography, in which evanescent fieldsemerging from the exit side of the objective can be used for imaging.

In FIG. 7, the region of the twofold beam folding and crossed beamguidance of a catadioptric projection objective 600 having a singleconcave mirror and 1-folding is shown. Corresponding elements bear thesame designations as in FIG. 2, increased by 500. As in the precedingembodiments, the radiation coming from the object plane 601 firstlystrikes the first folding mirror 606, which deflects the radiation awayfrom the optical axis 610 in the direction of the concave mirror (notshown), which reflects the radiation toward the second folding mirror608. The optical components serving to form the intermediate image 602,which also include a positive lens 652 arranged in the space betweenobject plane and first folding mirror, are designed such that theintermediate image is located in the direction in which the light runsbehind the second folding mirror 608, in front of the first lens 656 ofthe refractive second objective part. The geometric distance of theintermediate image to the inner edge 615, facing the axis, of the firstfolding mirror, as in the embodiments according to FIG. 2, is only afraction of about 20-30% of the meridonal extent of the intermediateimage, so that there is high geometric proximity. As distinct from theprevious embodiments, the intermediate image is not arranged in thespace between the critical mirror edge 615 and the object plane,however, but approximately at the axial height of the inner mirror edge615, beside the latter. The crossed beam guidance of the first beamsection (between object plane 601 and concave mirror) and of the secondbeam section (between concave mirror and image plane) with a cross-overregion geometrically between the positive lens 652 and the first foldingmirror 606, in conjunction with the proximity of the intermediate imageto the critical mirror edge 615, permits a high image-side numericalaperture which, in the example, is NA=0.8. The specification of thisdesign in detail can be taken from the European patent Application EP 1115 019 A2, whose disclosure content is made the content of thisdescription by reference (cf. FIG. 11 there).

By using FIG. 8, it will be explained, by way of example, that theinvention can also be used with advantage in other catadioptricprojection objectives having a single concave mirror and a single realintermediate image. The optical structure of the projection objective700 with respect to sequence and layout of the lenses along the opticalaxis can be taken from U.S. Pat. No. 6,195,213 B1, which in FIG. 2 andtable 1 shows a corresponding optical system with conventionalh-folding. The disclosure content in this respect is made the content ofthis description by reference.

The projection objective 700 is built up in such a way that theradiation coming from the object plane 701 firstly strikes the concavemirror 705, from which it is reflected in the direction of the firstfolding mirror 706. The latter is arranged with a reflecting surfacefacing the optical axis 710 such that the radiation is reflected in thedirection of a second folding mirror 708, which follows without anyinterposed lenses and deflects the radiation in the direction of thelenses of the refractive objective part 707. Since the first foldingmirror 706 is arranged on the side of the optical axis 710 that islocated opposite the refractive objective part 707 and the radiationcoming from the object field on its way to the concave mirror initiallypasses the first deflection mirror 706 on its side facing the secondobjective part, the second beam section leading from the concave mirrorvia the folding mirror 706 to the image plane crosses the first beamsection leading from the object plane to the concave mirror in across-over region, which is located between the first and second foldingmirror in the vicinity of the first folding mirror 706. The intermediateimage 702 is produced immediately in front of the first folding mirror.

The crossed beam guidance in the case of h-folding has a number ofadvantages as compared with the conventional arrangement of the foldingmirrors. From the point of view of mounting technology and mechanics, itis beneficial that the first folding mirror 706 is located on the sideof the optical axis 710 facing away from the second objective part 707.As a result, a stable fixing is possible with the aid of a compactfixing construction fitted to the rear side of the mirror on a mountingelement which can be fitted stably with the lens mounts of the opticalcomponents located in front of and behind the first folding mirror. Froma mechanical-optical point of view, care must be taken that, in thecrossed beam guidance according to the invention, the first foldingmirror in relation to the part of the optical axis running between theobject plane and concave mirror is on the side facing away from thesecond objective part 707, which corresponds to an arrangement of thefirst folding mirror on the (lower) side, facing away from the objectplane, of the horizontal section 710′ of the optical axis between thefirst folding mirror and the second folding mirror. In the case of thebeam guidance according to the invention, this horizontal part 710′ ofthe optical axis can be brought considerably closer to the reticle planethan in the case of conventional h-folding, in which the horizontal partof the optical axis is located geometrically between the first foldingmirror and the concave mirror, that is to say on the side of the firstfolding mirror facing away from the reticle. By displacing thehorizontal part of the optical axis in the direction of the objectplane, a reduction in the geometric optical conductance (etendue) can beachieved, since the critical (inner) edge of the folding mirror can bebrought closer to the reticle plane.

By using the following figures, exemplary embodiments of catadioptricprojection objectives according to the invention having more than onereal intermediate image and more than one concave mirror will beexplained. These are distinguished, inter alia, by the fact that, with abeneficial design, they permit good correction of image errors, inparticular it being possible to achieve effective correction of thePetzval sum (that is to say the image field curvature) and chromaticaberrations under conditions which are beneficial to fabrication.

FIG. 9 a shows an embodiment of a projection objective according to theinvention having two catadioptric objective parts, two refractiveobjective parts and precisely three real intermediate images. FIG. 9 bshows a detailed view of the region of the beam deflection device(folding device). The crossed beam path can be seen particularly well inthis illustration.

The immersion projection objective 800 has between its object plane 801and the image plane 803, in this order, a first dioptric objective part805, a first catadioptric objective part 806 having a first concavemirror 807 and an associated folding mirror 808, a second catadioptricobjective part 809 having a second concave mirror 810 and an associatedfolding mirror 812, and also a second refractive objective part 815.From the reticle (object plane 801, shown on the left in the figure),the light passes through the first refractive objective part 805, whichforms the first intermediate image 820. After that, the light strikesthe first folding mirror 808 in the light passage direction, which isimmediately behind the first intermediate image, in the vicinity of thelatter, and deflects the light in the direction of the first concavemirror 807. The associated catadioptric objective part 806, which pointsdownward in the drawing, can be aligned substantially horizontally inoperation. Such objective parts are also designated a horizontal arm(HOA) here. The catadioptric objective part 806 projects the light ofthe first intermediate image onto a second intermediate image 830, whichis located in the vicinity of the first folding mirror 808. Moreprecisely, the second intermediate image is located in the vicinity ofan inner mirror edge 811, facing the optical axis 810, of the firstfolding mirror 808, in the geometric space between this edge and thelast lens 812 of the first refractive objective part 805. From thesecond intermediate image 830, the light passes through the secondcatadioptric objective part 809, which forms a third intermediate image840 on the return path from the concave mirror 810, said image beinglocated immediately in front of the second folding mirror 812. By meansof the second refractive objective part 815, the third intermediateimage 840 is projected directly, that is to say without a furtherintermediate image, onto the wafer arranged in the image plane 803.

In FIG. 9 it is possible to see particularly well that the beam path 860leading from the object plane 801 of the first concave mirror 807, andthe second beam path 861 leading from the first concave mirror 807 tothe following objective part and finally to the image plane, cross inthe vicinity of the first folding mirror 808, approximately in theregion of the first intermediate image. The further course of the beamafter the second intermediate image is then free of any crossing.

This cross-like structure with two coaxial concave mirrors has preciselythree real intermediate images. There therefore exist four possiblepositions for aperture stops bounding beams (real pupil positions),mainly in the first refractive objective part 805, in the vicinity ofthe concave mirrors 807 and 810, and in the second refractive objectivepart 815. In this specific exemplary embodiment, the aperture stop 870is located in the first refractive objective part.

The folding mirrors 808, 812 are in each case located in the geometric(physical) vicinity of the intermediate images, which minimizes theoptical conductance, so that the object field can be arranged minimallyextra-axially. The intermediate images, that is to say the entire regionbetween the paraxial intermediate image and the marginal rayintermediate image, do not lie on the mirror surfaces, however, so thatpossible errors in the mirror surfaces are not projected sharply intothe image plane. In this case, the first and the third intermediateimages are in each case located both optically and geometrically in theimmediate vicinity of the most closely situated folding mirror, whilethe second intermediate image 830, although it is located geometricallyin the immediate vicinity of the inner mirror edge 811, is locatedoptically approximately centrally between the concave mirrors 807 and810.

The reflecting surfaces of the folding mirrors in this embodiment are ineach case inclined at 45° with respect to the optical axis, so that thefolding angles are exactly 90°. This rectangular folding is beneficialto the performance of the reflective layers of the folding mirrors.

The reticle plane 801 (plane of the object field) is not affected by themounting technology. In particular, there is a large spacing from theconcave mirrors, on account of the first relay system 805. No cut-offlenses are necessary, so that all the lenses can be formed as roundlenses.

The specification of the design is summarized in tables 5 and 6 intabular form and conventional notation. The system, designed as acatadioptric immersion objective, with a full field of 26·5.5 mm² andextremely pure water as immersion liquid, reaches an image-sidenumerical aperture NA=1.3. The projection objective per se is notaperture-limited, since there is beneficial folding geometry with anintermediate image in the vicinity of a folding mirror. Higherapertures, for example NA=1.35 or NA=1.4 or NA=1.5 or NA=1.7, areavailable if more highly refractive immersion media are used. Thediagonal ratio between the length of a diagonal of a minimum circlecentered in relation to the optical axis and enclosing the object fieldand the length of a diagonal of the object field (cf. FIG. 3) is about1.17. The wavefront aberrations are 7.5 mλ. In embodiments for 193 nm,all the lenses consist of silicon dioxide. The optically free lensdiameters are considerably less than 300 mm. The mass of the rawmaterial (raw compound) necessary for lens production is lower ascompared with conventional refractive systems or conventionalcatadioptric systems mentioned at the beginning having h-folding or1-folding, which represents a considerable improvement.

In the following text, further special features will be indicated which,in each case individually or in combination with other features, can bebeneficial in this and in other embodiments. The design contains fourfield lenses or field lens systems 812, 885, 886/887, 888 with apositive refractive power, which are in each case arranged in theimmediate vicinity of the folding mirrors and the intermediate images.In at least one of the catadioptric horizontal arms, there should be anegative lens, in order to ensure the chromatic correction. Preferably,at least one negative lens 890, 891, 892 is provided in eachcatadioptric objective part, preferably in the immediate vicinity of theconcave mirror. Beneficial variants include at least three lenses whichare passed through twice. In the exemplary embodiment shown, there aresix lenses which are passed through twice, namely the field lenses 885,886, 887 and the negative lenses 890, 891, 892 in front of the concavemirrors for the chromatic correction of the longitudinal color error.

Beneficial variants include little negative refractive power in therefractive objective parts, which means that the lens diameters of theseparts can be kept small overall. In the exemplary embodiment, only inthe second refractive objective part 815 is a biconcave negative lens880 provided in the divergent beam path on the input side of theobjective part, at the exit side of which high angles of incidencebeneficial to the correction occur.

The design exhibits high coma in the intermediate images, in particularin the third intermediate image 840. This helps to correct the sinecondition in the image space without surfaces with excessively highangles of incidence in the second refractive objective part 815.

Numerous variants are possible. In this regard, FIG. 10 shows, by way ofexample, an optically identical variant of a projection objective 800′having catadioptric subsystems inclined obliquely with respect to theoptical axis for more beneficial reflecting layers. In the embodimentshown, the horizontal arms continue to be coaxial but are inclined by20° with respect to a vertical alignment. The angles of incidence at thefolding mirrors can thus be reduced.

It is also possible to design projection objectives according to theinvention as a dry objective. FIG. 11 shows, by way of example, aprojection objective 900 having an image-side numerical aperture NA=0.95and a finite working distance at the wafer. In dry systems, the spacebetween the objective exit face and the wafer is filled with a gasduring operation. System data for the cross-like dry system in FIG. 11is specified in tables 7 and 8. In this system, at individual surfacesof the second refractive objective part, in particular at the exit faceof the input-side biconcave negative lens and at the exit face of theobject-side concave negative meniscus lens, very high angles ofincidence, which contribute effectively to the correction, occur in theimmediate vicinity of the pupil face situated most closely to the image.

The embodiments shown in FIGS. 9 to 11 are designed such that the twoflat folding mirrors are positioned at a short distance from each other,back to back, that is to say with reflecting surfaces facing away fromeach other. Under certain circumstances, this can be achieved by meansof a single, double-silvered element which can have the form of aplane-parallel plate. In principle, it is also possible for the beamdeflection to be carried out with a solid material prism, as shown inFIG. 12. In this case, the light coming from the object plane firstlyenters the folding prism 895 and the first folding reflection takesplace at the hypotenuse face 896 of the prism. After passing through thefirst catadioptric objective part and the second catadioptric objectivepart, the second folding reflection takes place at the same hypotenuseface, but on its rear side. In the embodiment shown in FIG. 12, a firstbeam path leads from the object plane (not shown) via the first foldingmirror (inner side of the hypotenuse face) and the first concave mirror(not shown, arranged at the bottom in the figure) to the second concavemirror (not shown, located at the top in the figure), and the secondbeam section, after reflection at the second concave mirror, leads viathe second folding mirror (outer side of the hypotenuse face) in thedirection of the image plane. In this case, the crossing of the beampaths takes place immediately after the reflection at the second foldingmirror and the formation of the third intermediate image, in theimmediate vicinity of the reflecting surface of the second foldingmirror, between the latter and the first lens of the following, secondrefractive objective part.

For the case in which calcium fluoride is selected for the deflectionprism, for reasons of laser resistance, care must be taken that, withits refractive index of n≈1.50 at 193 nm and the numerical aperture ofabout NA=0.3 present at the intermediate image, total reflection overthe entire beam cross section is not to be expected. It is thereforebeneficial to apply a powerful reflective layer, reflecting on bothsides, to the hypotenuse face. However, it is also possible to enlargethe folding angle in the prism in such a way that total reflectionoccurs at the hypotenuse face for all incident rays. It is then possibleto dispense with a reflective coating.

Within the scope of this cross-like design, numerous variants arepossible. For example, it is possible to provide different projectionscales, for example reduction scales of 4:1, 5:1 or 6:1. Higherprojection scales (for example 5:1 or 6:1) can be more beneficial, sincethey reduce the object-side aperture and can thus relax the requirementson the folding geometry.

The first refractive subsystem, serving as a relay system, which formsthe first intermediate image, has a projection scale β close to 1 in theexemplary embodiments. However, this is not imperative. It is equallynot very necessary for the catadioptric objective parts to haveprojection scales in the region of 1. Here, a magnifying projectionscale of the first objective part can be beneficial to relaxing therequirements on the folding geometry.

In the above examples of catadioptric systems having three intermediateimages and two catadioptric subsystems, the refractive front system(first subsystem, relay system) is constructed asymmetrically. Thedistance between the two planar folding mirrors should be small, inorder that the distance of the extra-axial object field from the opticalaxis remains as small as possible with vignetting-free projection, andthus reduce the requirements on the optical design for achieving a smalletendue or a small superfield. In addition, the object-image shift(OIS), that is to say the lateral offset between the object-side opticalaxis and image-side optical axis, then remains small.

By using FIG. 13, a variant of a cross-like catadioptric system 1000having two concave mirrors and three intermediate images will be shown,being distinguished by a largely symmetrical structure. It has, betweenits object plane 1001 and its image plane 1002, a first refractiveobjective part 1010, which forms a first intermediate image 1011, afirst catadioptric objective part 1020, which forms a secondintermediate image 1021 from the first intermediate image, a furthercatadioptric objective part 1030, which forms a third intermediate image1031 from the second intermediate image, and a fourth, refractive objectpart 1040, which projects the third intermediate image into the imageplane 1002. All the objective parts have a positive refractive power.Lenses or lens groups with a positive refractive power are representedby double arrows with points aimed outward, lenses or lens groups with anegative refractive power, on the other hand, are represented by doublearrows with points aimed inward.

A first beam section 1050 runs from the object plane 1001 via the firstfolding mirror 1055 and the associated concave mirror 1025 following inthe light path to the concave mirror 1035 of the second catadioptricobjective part 1030. A second beam section 1060 runs from this concavemirror 1035 via the second folding mirror 1065 to the image plane. Onthe way from the second folding mirror to the image plane, the secondbeam section crosses the first beam section in the region in front ofthe reflecting surface of the second folding mirror.

The first objective part 1010 comprises a first lens group LG1 with apositive refractive power and a second lens group LG2 with a positiverefractive power. Between these two lens groups, the main beamintersects the optical axis at the point of a preferred aperture stopplane (system aperture stop) 1070.

The first lens group LG1 preferably comprises at least two positivelenses, namely at least one lens L1 close to the field and at least onelens L2 close to the aperture. This applies in a corresponding way tothe lens group LG2, which preferably has at least one lens L4 close tothe field and at least one lens L3 close to the aperture.

Meeting the following conditions, individually or in combination, can bebeneficial to simplifying the fabrication of the system:

LG1=LG2; L1=L2=L3=L4; L1=L4; L2=L3.

In these equations, the equality of two lenses is to be understood tomean equality of their radii. The lenses can therefore have unequalthicknesses. The equality of radii is not to be understood to bemathematically exact but, from a fabrication point of view, that thelens faces should be capable of production with the same tool. For theequality of lens groups, appropriate boundary conditions apply. Suchsystems offer advantages in fabrication, since the production andtesting of the lenses are simplified.

The arrangement of the lenses can be symmetrical or asymmetrical inrelation to planes perpendicular to the optical axis. Here, asymmetrical structure with reference to the aperture stop plane 1070 isbeneficial. In advantageous embodiments, the aperture stop is fitted inthis aperture stop plane for the purpose of variable limiting of thebeam diameter. This is beneficial since, as a result, no asymmetricalimage errors are introduced into the first intermediate image 1011.

The projection scale P of the first objective part 1010 can be aboutβ=1. Although the first subsystem 1010 is constructed largelysymmetrically, it is operated asymmetrically, that is to say with β≠1.The advantage of this quasisymmetrical arrangement is the introductionof a value which is advantageous for the further correction of thechromatic magnification difference (transverse color error), and otherasymmetrical image errors, primarily coma.

The objective can have one or more aspherical faces. The lens L1arranged close to the field preferably bears at least one asphericalface in order to correct the telecentering in the object space.Alternatively or additionally, one of the lenses L3 and/or L4 can bearat least one aspherical face in order to correct the sphericalaberration in the first intermediate image. This relieves the foldinggeometry stress and permits a small etendue (optical conductance).

The first objective part 1010 is preferably constructed with “a lowPetzval”, that is to say with lenses with a reduced Petzval sum. A “lowPetzval” structure can be produced if lenses with a small Petzval sumare employed, in particular suitable meniscuses. The telecentering,spherical aberration and astigmatism can be corrected by means ofaspheres on the lenses L1 and L2 or L3 and L4.

In general, in these and in the other embodiments, the optical distancebetween a reflecting surface of a folding mirror and the most closelysituated intermediate image should lie between a finite minimum distanceand a maximum distance. The maximum distance can, for example, be 1/10or 1/15 or 1/20 of the system length (overall length, distance betweenobject plane and image plane). The minimum distance should be small incomparison with this.

It is beneficial if the first objective part 1010 is over-correctedspherically if the first folding mirror 1055 is situated behind theparaxial intermediate image 1011, and is under-corrected spherically ifthe paraxial intermediate image is situated behind the folding mirror.This ensures that the intermediate image does not lie on the reflectingsurface.

The Petzval sum is preferably set such that the focus of the outermostfield point and of the innermost field point are located virtually atthe same distance from the first folding mirror. The intermediate imagecan then be moved close to the reflecting surface, since the curvedimage field curves away from the reflecting surface. This relaxes therequirements on the folding geometry and permits a small etendue.

The catadioptric objective parts 1020, 1030 are preferably constructeddoubly telecentrically. This permits the correction of the astigmatismin the second and third intermediate image.

It is possible that the first objective part 1010 has no negativelenses. In some embodiments, provision is made to correct the Petzvalsum in the refractive first objective part 1010 as well or to reduce itsharply. Negative lenses close to the object or close to the image canbe used for this purpose.

The catadioptric objective parts 1020, 1030 are preferably constructedaxially symmetrically, so that all the lenses are used with a doublepassage. It is beneficial if they comprise a positive lens group LG4 orLG5 in the vicinity of the corresponding intermediate image, and anegative lens group LG3 or LG6 in the vicinity of the concave mirror.The positive lens groups LG4, LG5 preferably have one or two positivelenses, the negative lens groups LG6, LG3 have a maximum of threenegative lenses. In some embodiments, it is possible to dispense withnegative lenses in one of the catadioptric objective parts.

A symmetrical structure of the catadioptric parts can be beneficial. Itis preferable if, according to the above explanations, the followingconditions are met, alternatively or in combination: LG4=LG5; LG3=LG6;and M1=M2, where M1 and M2 are the concave mirrors 1020, 1035. Theequality of the optical components is to be understood in the sense ofthe above definition of equality of radii. In the case of a symmetricalstructure, the aberration load (Petzval and longitudinal color errorCHL) is distributed substantially uniformly to the two catadioptricobjective parts. This structure can be very advantageous, since therefractive powers and, as a result, the aberration contributions can beminimized.

It can be beneficial to operate the catadioptric objective parts 1020,1030 quasi-symmetrically, that is to say with a projection scalediffering slightly from β=1. This permits simple correction of thetransverse color error (CHV) for the overall system.

In another preferred arrangement, the positive lens groups LG4, LG5 eachcomprise two positive lenses, which can in particular be identical. Thisrelaxes the requirements on the aberration contributions of these lensgroups.

It can be beneficial if the catadioptric objective parts 1020, 1030 areconstructed such that the Petzval sum of the refractive lens elements ofthe lens groups LG3 and LG4 in the first catadioptric objective part1020, and LG5 and LG6 in the second catadioptric objective part 1030compensate one another, largely or completely. Then, the Petzvalcontribution of the concave mirrors 1025, 1035 primarily remains for thecompensation of the Petzval curvature of the objective parts.

In the catadioptric parts, one or more aspherical faces can be provided.This permits or assists a correction in the second and thirdintermediate image, and thus permits relaxation of the requirements onthe folding, and also a reduction in the optical conductance.

The refractive objective part 1040 is preferably constructed from threelens groups, namely a first lens group LG7 close to the field and asecond and third lens group LG8 and LG9, between which the main beamcuts the optical axis, so that a preferred aperture stop plane isproduced here. Lens group LG8 in front of the system aperture stoppreferably has at least one face curved toward the image plane with highbeam angles, for example an image-side lens face of a negative meniscuslens or a negative biconcave lens. This contributes substantially to thecorrection of the sine condition. No lens group should be arrangedbetween the aperture stop position and the image plane, that is to sayin the lens group LG9. It is beneficial if the last two or more lenselements consist of calcium fluoride with various crystal orientations,by which means compaction problems can be avoided and, at the same time,influences of the intrinsic birefringence can at least partly becompensated for.

The two plane-parallel folding mirrors 1055, 1065 can be provided on asingle plane-parallel plate reflective on both sides. This shouldconsist of a highly transparent material. This permits simple testing ofthe parallelism before coating with reflective layers. Preferredmaterial for the substrate is silicon dioxide. As a result of a smalldistance between the folding mirrors, a reduction in the objectiveetendue (and in the object image shift) is possible.

Within the scope of the invention, systems having more than threeintermediate images are also possible. As a result, further degrees ofdesign freedom for optimizing the space required and the opticalcorrection can be created. The projection objective 1100 in FIG. 14 hasbetween its object plane 1101 and the image plane 1102 a firstrefractive subsystem 1110 for forming a first real intermediate image1111, a first catadioptric objective part 1120 for forming a second realintermediate image 1121 from the first intermediate image, a secondrefractive subsystem 1130 for forming a third intermediate image 1131from the second intermediate image, a further catadioptric objectivepart 1140 for forming a fourth intermediate image 1141 from the thirdintermediate image, and a third refractive objective part 1150 whichprojects the fourth intermediate image into the image plane 1102. Thefirst catadioptric objective part 1120 comprises a first folding mirror1122 for deflecting the radiation coming from the object in thedirection of the concave mirror 1125, and the second catadioptricobjective part 1140 has a folding mirror 1142 which is assigned to theconcave mirror 1145 and deflects the radiation coming from the concavemirror 1145 in the direction of the image plane.

In the region of the first catadioptric objective part, a first beamsection 1160 leads from the object plane via the first folding mirror1122 to the concave mirror 1125, and a second beam section 1170 leadsfrom the latter to the following objective parts. The two beam sectionscross one another in the vicinity of the object-side mirror edge, facingthe first objective part 1110, of the folding mirror 1122. A symmetricalsituation results in the second catadioptric objective part 1140. Theradiation passing from the object plane to its concave mirror 1145 formsa first beam section 1170, the radiation reflected from the mirror 1145and deflected by the plane mirror 1142 in the direction of the imageplane forms a second beam section 1180, which crosses the first beamsection in a cross-over region between the folding mirror 1142 andrefractive subsystem 1150. The overall projection objective can havesubstantially a point-symmetrical structure, in which the point ofsymmetry lies within the central relay system 1130.

The entry-side and exit-side refractive systems 1110 and 1150 in eachcase have a projection scale β≈1, and this is also true of thecatadioptric objective parts 1120 and 1140. The refractive relay system1130, which transfers the radiation from the first catadioptricsubsystem 1120 to the second catadioptric subsystem 1140 with aprojection, has a projection scale in the region of 1:3 to 1:6. Thisreduction also corresponds to the overall reduction of the projectionobjective. In the basic structurerefractive-catadioptric-refractive-catadioptric-refractive, the axialorientation can be set as required by means of suitable alignment of thefolding mirrors.

The aberration compensation proceeds in a similar way to that in thepreceding examples. The series of continuous lines corresponds to themain ray of the outer field point.

In the system in FIG. 14, the optical axes of the catadioptricsubsystems 1120 and 1140 run coaxially, so that an inclination of one ofthe axes defines the inclination of the other axes. If, for example, oneaxis is inclined in order to create space, the other axis may also beinclined such that space is restricted. In the following text, exemplaryembodiments of how such problems can be avoided will be shown. They canbe used as self-contained projection objectives or as subsystems withina more complex catadioptric structure.

From the point of view of the basic structure, the projection objective1200 in FIG. 15 represents a combination of a catadioptric projectionobjective 1210 with 1-folding and two folding mirrors fitted to a mirrorprism (cf. FIG. 5) and a following catadioptric subsystem 1220 withmodified 1-folding and crossed beam path (for example according to FIG.4). The first catadioptric subsystem 1210 forms a real intermediateimage 1202 from the extra-axial field, which is arranged in its objectplane 1201. This intermediate image is projected into the image plane1203 of the system by the second catadioptric subsystem 1220.

The object plane 1201 of the system shown can be the object plane of theentire projection objective or an intermediate image plane, in whichthere is situated an intermediate image which is formed by a subsystemconnected upstream but not shown in FIG. 15. FIG. 16 shows, by way ofexample, such a structure, which is provided in a refractive subsystem1250, serves as a relay system and forms a real intermediate image ofthe object plane 1290 in the plane 1201. This is used as the object ofthe following catadioptric system according to FIG. 15, which comprisestwo axially offset concave mirrors.

In both the embodiments, a first beam section leads via multiple foldingto the concave mirror 1221 of the second catadioptric objective part1220, while a second beam section runs from this mirror via the secondfolding mirror 1242 to the image plane 1203. In the geometric spacebetween the exit-side folding mirror 1212 of the first catadioptricobjective part and the first folding mirror 1222 of the secondcatadioptric objective part 1220, the first beam path and the secondbeam path cross behind the intermediate image 1202.

The projection system shown in FIG. 15, which can be a self-containedprojection objective or a subsystem within a larger projection objective(cf. FIG. 16), has two real intermediate images 1202, 1232. The opticalaxes of the catadioptric objective parts 1210, 1220 are decoupled fromeach other, that is to say are not coaxial with each other but offsetlaterally parallel to each other. The catadioptric subsystems are ineach case constructed axially symmetrically. Each includes a positivelens group close to the object and a negative lens group close to theconcave mirror. Therefore, positive refractive power is arranged in thevicinity of the intermediate images and of the folding mirrors here too,while negative refractive power is concentrated in the vicinity of theconcave mirrors.

As shown in FIG. 16, the subsystem illustrated in FIG. 15 can be used toproject the intermediate image of the object field formed by a relaysystem 1250 into the image plane of the projection objective. Theoverall system then has three intermediate images.

Another variant provides that, in this system, the optical axes of themirror groups can both be inclined in the direction of the wafer plane.This increases the space between the concave mirror of the firstcatadioptric objective part and the reticle plane or intermediate imageplane 1201.

All the embodiments illustrated by way of example can be incorporated inthe projection exposure machine shown in FIG. 1 instead of theprojection objective 5. In the case of wafer scanners, care must betaken that the drive for the movements of the device 40 for holding andmanipulating a mask (reticle stage) and the device 50 for holding andmanipulating the wafer (wafer stage) must be matched to the type ofcatadioptric projection objective. Depending on the number of foldingmirrors, concave mirrors and intermediate images, the drive must beconfigured such that either a scanning movement of reticle and waferstage in the same direction or a movement of reticle and wafer stage inopposite directions takes place during scanning. If the sum S of thenumber Z of intermediate images, the number F of folding mirrors and thenumber K of concave mirrors is an uneven number, then a scanningmovement in the same direction must be provided; if the sum S is an evennumber, then a scanning movement in opposite directions must beproduced. Therefore, in the embodiments explained by using FIGS. 9, 10,11, 12, 13 and 16, a scanning movement in the same direction must beprovided, while in the embodiments according to FIGS. 2, 6, 7, 8, 14 and15, reticle and wafer must be moved in opposite directions in relationto each other along the y axis.

TABLE 1 Face Radii Thicknesses Material Index ½ diameter 1 0.0000000.000000 AIR 79.675 2 0.000000 10.000000 SIO2HL 1.56018811 79.675 30.000000 1.000000 AIR 81.476 4 319.475286 20.000234 SIO2HL 1.5601881185.084 5 995.269474 68.424969 AIR 85.919 6 0.000000 169.872505 AIR95.577 7 −970.753457 44.999585 SIO2HL 1.56018811 119.609 8 −327.540786217.911147 AIR 123.649 9 −231.387741 17.500000 SIO2HL 1.56018811 125.41610 −1065.062890 48.294619 AIR 135.575 11 −196.821494 17.500000 SIO2HL1.56018811 136.404 12 −525.772724 32.979078 AIR 160.520 13 0.0000000.000000 REFL 204.292 14 264.796887 32.979078 REFL 162.687 15 525.77272417.500000 SIO2HL 1.56018811 160.034 16 196.821494 48.294619 AIR 132.91517 1065.062890 17.500000 SIO2HL 1.56018811 130.452 18 231.387741217.911147 AIR 117.791 19 327.540786 44.999585 SIO2HL 1.56018811 101.59920 970.753457 181.477269 AIR 96.159 21 0.000000 128.395393 AIR 61.789 220.000000 24.998738 AIR 110.784 23 312.774233 50.000130 SIO2HL 1.56018811135.026 24 −938.039680 2.332118 AIR 135.592 25 715.324368 28.435222SIO2HL 1.56018811 135.878 26 −1554.047709 0.949762 AIR 135.289 27626.921957 28.002516 SIO2HL 1.56018811 132.433 28 −1428.035483 37.991193AIR 130.956 29 −309.156200 9.521188 SIO2HL 1.56018811 125.631 30−562.362375 181.567266 AIR 125.277 31 −173.995248 9.499422 SIO2HL1.56018811 99.321 32 247.888809 29.437283 AIR 109.165 33 8340.11772532.129675 SIO2HL 1.56018811 111.460 34 −312.940978 7.464540 AIR 116.08235 929.377252 44.625129 SIO2HL 1.56018811 132.361 36 −333.5129130.949477 AIR 134.568 37 591.097249 44.418308 + C2 SIO2HL 1.56018811140.004 38 −1614.017804 24.278142 AIR 140.003 39 0.000000 −23.329538 AIR138.515 40 302.573027 9.498538 SIO2HL 1.56018811 139.988 41 225.45282923.324104 AIR 137.709 42 374.450165 43.305784 SIO2HL 1.56018811 138.65843 −1347.892608 0.947859 AIR 139.026 44 302.595256 44.140336 SIO2HL1.56018811 139.127 45 −12394.382724 0.947473 AIR 137.426 46 220.76154240.029388 SIO2HL 1.56018811 125.456 47 809.070272 0.946947 AIR 121.41948 163.063737 40.300977 SIO2HL 1.56018811 103.421 49 762.111474 0.946425AIR 96.933 50 139.902742 77.435206 SIO2HL 1.56018811 75.207 51 0.0000002.000000 H2OV193 1.43667693 19.413 52 0.000000 0.000000 AIR 17.000

TABLE 2 5 8 = 19 10 = 17 12 = 14 27 K  0  0  0  0  0 C1 −1.188191E−08 3.591288E−09 −4.791180E−09 −8.429951E−10 −5.683539E−09 C2  1.967391E−13−3.350971E−14  6.912483E−14 −5.232984E−15  6.541643E−15 C3 −7.746732E−18 1.502596E−18  2.275816E−19 −3.132061E−19 −2.750649E−19 C4  4.382264E−23 2.954168E−23  1.312434E−22 −2.344674E−23  5.788139E−23 C5  4.532193E−26−6.493001E−28 −4.748900E−27  6.334947E−28 −2.220373E−27 C6 −3.233502E−30 3.320789E−32  1.399914E−31 −1.231728E−32  8.916186E−32 33 35 37 47 K  0 0  0  0 C1 −8.560622E−09 −2.328354E−08  1.335791E−09 −1.418195E−08 C2−1.349963E−12  2.144034E−12 −8.0567246−13  1.409773E−12 C3  1.587936E−16−1.398657E−16  4.148247E−17 −6.196993E−17 C4 −8.008240E−21  5.252748E−21−9.137514E−22  1.830118E−21 C5  2.874374E−25 −1.188241E−25  1.616592E−26−3.946542E−26 C6 −6.218920E−30  1.696094E−30 −2.274089E−31  2.728014E−31

TABLE 3 Face Radii Thicknesses Material Index ½ diameter 1 0.0000000.000000 AIR 74.869 2 0.000000 10.000000 SIO2 1.56097018 74.869 30.000000 0.500000 AIR 76.658 4 3088.172820 10.000000 SIO2 1.5609701876.952 5 0.000000 60.000000 AIR 78.641 6 0.000000 0.000000 AIR 95.735 70.000000 134.465366 AIR 95.735 8 302.601867 34.401664 SIO2 1.56097018144.675 9 705.234819 68.979243 AIR 144.202 10 251.382127 33.175965 SIO21.56097018 149.996 11 426.058169 289.332591 AIR 147.417 12 −260.11269720.000000 SIO2 1.56097018 121.372 13 −572.625245 42.216988 AIR 125.40714 −171.019518 20.000000 SIO2 1.56097018 125.493 15 −855.92438237.063295 AIR 149.787 16 0.000000 0.000000 REFL 192.254 17 264.44725937.063295 REFL 151.718 18 855.924382 20.000000 SIO2 1.56097018 150.21719 171.019518 42.216988 AIR 124.976 20 572.625245 20.000000 SIO21.56097018 124.607 21 260.112697 289.332591 AIR 118.964 22 −426.05816933.175965 SIO2 1.56097018 123.141 23 −251.382127 68.979243 AIR 125.54224 −705.234819 34.401664 SIO2 1.56097018 114.138 25 −302.601867148.236577 AIR 113.753 26 0.000000 76.228794 AIR 65.370 27 0.0000000.000000 AIR 87.565 28 0.000000 201.841415 AIR 87.565 29 1761.16681750.475596 SIO2 1.56097018 148.012 30 −358.244969 284.608494 AIR 149.87231 303.934833 35.000000 SIO2 1.56097018 147.098 32 509.533530 7.170752AIR 143.625 33 370.904878 20.000366 SIO2 1.56097018 142.151 34211.313761 62.331548 AIR 133.109 35 290.910582 56.153178 SIO2 1.56097018138.951 36 −1106.757797 68.197851 AIR 137.608 37 −178.117460 59.999881SIO2 1.56097018 133.318 38 −214.351289 −12.849220 AIR 148.117 390.000000 24.486144 AIR 141.938 40 277.046273 63.368104 SIO2 1.56097018144.287 41 −757.891281 0.999992 AIR 142.301 42 127.447162 72.144248 SIO21.56097018 110.531 43 316.261462 0.099994 AIR 92.548 44 137.33484247.277234 SIO2 1.56097018 81.195 45 210.414165 0.999989 AIR 54.341 46110.455126 44.071322 SIO2 1.56097018 48.586 47 0.000000 0.000000 SIO21.56097018 16.000 48 0.000000 0.000000 AIR 16.000

TABLE 4 Face 4 8 = 25 11 = 22 13 = 20 29 31 K  0  0  0  0  0  0 C1−1.17E−08  7.10E−10  4.43E−09 −7.25E−09  2.55E−10  9.67E−09 C2 −5.58E−14 1.16E−14 −4.74E−14  2.48E−14 −6.17E−14 −7.64E−13 C3 −6.44E−18  8.33E−19 1.40E−18  1.28E−20 −6.21E−20  1.96E−17 C4 −4.47E−23 −4.54E−23 −5.27E−24−1.12E−22  2.57E−23 −7.03E−22 C5 −7.31E−27  1.09E−27 −6.31E−28  8.33E−27−4.83E−28  1.82E−26 C6  3.72E−32 −1.31E−33  2.42E−32 −1.64E−31 −1.36E−33 1.31E−31 Face 33 35 40 43 45 K  0  0  0 0  0 C1 −3.12E−08  9.65E−09−7.80E−09  3.26E−08  8.42E−08 C2  1.51E−12 −6.13E−13  1.23E−13 −5.62E−13 1.69E−11 C3 −2.25E−17  8.81E−18 −3.25E−19  4.68E−17 −1.72E−16 C4−8.50E−23  3.92E−23 −6.27E−25 −1.11E−20  5.74E−19 C5  1.19E−26 −5.57E−27−3.07E−27  6.32E−25 −7.64E−23 C6 −6.28E−31  8.11E−32  5.63E−32 −8.86E−30 1.33E−26

TABLE 5 Face Radii Thicknesses Material Index ½ diameter 0 0.00000040.000000 63.000 1 0.000000 0.000000 74.812 2 280.911554 29.101593 SIO21.56029525 78.206 3 1315.382634 67.564457 79.868 4 1226.076021 36.889857SIO2 1.56029525 94.337 5 −224.620142 132.650952 95.649 6 132.55745037.873616 SIO2 1.56029525 81.937 7 −1652.923938 26.883045 78.866 80.000000 138.896699 67.638 9 175.542348 36.333740 SIO2 1.56029525 75.65110 −236.570865 100.002684 75.039 11 0.000000 9.995756 59.032 12 0.000000−81.094895 REFL 110.211 13 −208.565918 −48.990866 SIO2 −1.56029525104.471 14 517.535257 −178.645431 104.642 15 398.156640 −15.000000 SIO2−1.56029525 100.231 16 −950.114340 −73.251055 103.344 17 116.287221−15.000000 SIO2 −1.56029525 104.039 18 473.502609 −41.360609 140.152 19194.854755 41.360609 REFL 143.288 20 473.502609 15.000000 SIO21.56029525 139.289 21 116.287221 73.251055 99.401 22 −950.11434015.000000 SIO2 1.56029525 92.823 23 398.158640 178.645431 87.639 24517.535257 48.990866 SIO2 1.56029525 84.803 25 −208.565918 81.09701683.851 26 0.000000 84.970261 59.404 27 176.145326 23.179878 SIO21.56029525 79.591 28 756.736803 0.944155 79.800 29 314.641675 30.039119SIO2 1.56029525 80.579 30 −500.071834 218.126390 80.744 31 −108.65146015.000000 SIO2 1.56029525 80.556 32 −785.250977 30.057005 106.274 33−182.598151 −30.057005 REFL 109.565 34 −785.250977 −15.000000 SIO2−1.56029525 107.546 35 −108.651460 −218.126390 87.013 36 −500.071834−30.039119 SIO2 −1.56029525 88.079 37 314.641675 −0.944155 87.604 38756.736803 −23.179878 SIO2 −1.56029525 86.420 39 176.145326 −49.96514785.965 40 0.000000 −10.012234 62.226 41 0.000000 69.993842 REFL 66.12042 −340.701792 14.476713 SIO2 1.56029525 61.548 43 −198.092016 38.43349363.405 44 −681.785807 14.078463 SIO2 1.56029525 69.045 45 −317.00543227.751722 70.244 46 −110.357531 9.500172 SIO2 1.56029525 70.916 47311.065100 22.414990 86.590 48 −1344.254472 43.792412 SIO2 1.5602952590.705 49 −138.390126 5.810077 97.254 50 552.864897 42.476541 SIO21.56029525 127.381 51 −483.961511 63.875640 129.334 52 1021.98045938.430027 SIO2 1.56029525 142.111 53 −410.501933 0.936239 142.917 54578.822230 39.856519 SIO2 1.56029525 139.665 55 −723.060175 0.932875138.387 56 283.549462 33.604225 SIO2 1.56029525 124.246 57 1607.0802040.891917 120.727 58 167.944629 33.588386 SIO2 1.56029525 106.594 59370.375071 0.941416 101.486 60 94.822236 39.056245 SIO2 1.5602952580.000 61 175.331402 0.944860 70.631 62 58.889747 49.845949 SIO21.56029525 50.337 63 0.000000 2.000000 H2OV193 1.43682260 19.381 640.000000 −0.000335 H2OV193 1.43682260 15.750 65 0.000000 0.000335 15.750

TABLE 6 Face 3 7 9 14 = 24 18 = 20 K  0  0  0  0  0 C1  2.886968E−08 6.178555E−08 −1.273482E−07 −2.178828E−08  1.372393E−08 C2  1.135834E−12 6.960497E−13  4.938210E−12 −2.747119E−13 −3.413863E−13 C3  2.526440E−17−5.947244E−17 −3.380917E−16  2.007136E−17  1.076781E−17 C4 −2.060922E−21 3.751921E−20  1.794088E−20  1.731842E−21 −3.258468E−22 C5 −7.650561E−25−4.325897E−24 −7.057449E−25 −2.027055E−25  6.466061E−27 C6  5.723867E−29 7.686244E−29  2.539541E−30  5.423640E−30 −5.896986E−32 Face 28 = 38 32= 34 48 52 57 K  0  0  0  0  0 C1  7.190084E−08 −3.011106E−08−5.757903E−08 −3.792122E−08 −2.413143E−08 C2 −5.639061E−13  1.342687E−12 1.903176E−12  1.535276E−12  2.795676E−12 C3  9.086478E−18 −6.959794E−17−7.267601E−17 −1.992532E−17 −1.365078E−16 C4  8.555051E−22  3.712216E−21 1.940815E−21 −4.676144E−22  5.749863E−21 C5 −2.763206E−26 −1.392566E−25−1.899677E−25  2.069154E−26 −1.655627E−25 C6 −9.351012E−31  2.691744E−30−4.747025E−30 −2.314945E−31  2.725293E−30

TABLE 7 Face Radii Thicknesses Material Index ½ diameter 0 0.00000040.000000 63.000 1 0.000000 0.000000 72.900 2 169.031176 30.007246SIO2HL 1.56029525 77.565 3 172.807988 86.884665 76.339 4 262.43330142.053156 SIO2HL 1.56029525 100.639 5 −396.930898 170.685368 100.745 691.344099 19.740243 SIO2HL 1.56029525 71.904 7 105.469868 16.14217667.557 8 137.822248 20.121802 SIO2HL 1.56029525 65.141 9 591.27703320.282197 61.580 10 0.000000 102.718997 54.773 11 344.588322 32.632993SIO2HL 1.56029525 64.580 12 −119.973712 98.386450 64.972 13 0.00000010.002615 42.632 14 0.000000 −100.001190 REFL 118.932 15 −248.418133−48.786808 SIO2HL −1.56029525 101.847 16 260.257319 −174.240023 102.62317 751.662806 −15.000000 SIO2HL −1.56029525 96.605 18 −546.358993−49.118038 97.378 19 142.990930 −15.000000 SIO2HL −1.56029525 97.645 201260.283293 −34.592386 115.849 21 192.845940 34.592380 REFL 117.242 221260.283293 15.000000 SIO2HL 1.56029525 114.937 23 142.990930 49.11803891.181 24 −546.358993 15.000000 SIO2HL 1.56029525 86.779 25 751.662806174.240023 82.828 26 260.257319 48.786808 SIO2HL 1.56029525 78.494 27−248.418133 99.999230 75.744 28 0.000000 95.015900 42.841 29 177.68128730.008789 SIO2HL 1.56029525 65.929 30 −516.705121 171.287965 67.227 31217.817800 29.576821 SIO2HL 1.56029525 88.903 32 310.498099 41.61856086.845 33 −166.352653 15.000000 SIO2HL 1.56029525 86.950 34 439.16001939.859648 98.417 35 −192.193047 −39.859648 REFL 100.860 36 439.160019−15.000000 SIO2HL −1.56029525 99.124 37 −166.352653 −41.618560 87.790 38310.498099 −29.576821 SIO2HL −1.56029525 87.638 39 217.817800−171.287965 89.485 40 −516.705121 −30.008789 SIO2HL −1.56029525 64.34841 177.681287 −60.011782 62.727 42 0.000000 −9.997777 44.036 43 0.00000090.957117 REFL 58.394 44 144.598375 33.191986 SIO2HL 1.56029525 66.06545 −312.576397 52.726003 66.275 46 −107.389980 9.492973 SIO2HL1.56029525 62.695 47 165.658290 32.869123 71.558 48 −577.19223825.782062 SIO2HL 1.56029525 78.414 49 −150.951285 0.976825 84.261 5029506.35748 24.339009 SIO2HL 1.56029525 100.691 51 −374.391026 0.956935104.021 52 644.947215 57.187603 SIO2HL 1.56029525 113.079 53 −174.62392116.895926 114.436 54 1344.546605 39.235791 SIO2HL 1.56029525 103.044 55−218.318623 12.126286 101.595 56 −165.249581 9.493815 SIO2HL 1.5602952599.807 57 −529.158535 0.942157 101.677 58 199.277639 44.383379 SIO2HL1.56029525 100.857 59 — 7.470338 98.182 60 208.537801 18.754883 SIO2HL1.56029525 85.455 61 334.304631 5.703329 80.986 62 83.732122 29.895330SIO2HL 1.56029525 65.881 63 175.404465 0.950929 58.182 64 81.49187626.728679 SIO2HL 1.56029525 51.783 65 443.279667 3.284129 42.929 66 0 10SIO2HL 1.56029525 39.654 67 0 6 32.119 68 0 0 15.764

TABLE 8 Face 3 9 11 16 = 26 20 = 22 K  0  0  0  0  0 C1  3.188825E−08 5.249301E−08 −1.523480E−07 −2.416867E−08  2.294396E−08 C2  2.650655E−13 9.672904E−12  6.099552E−12 −5.962244E−13 −1.007737E−12 C3 −6.675542E−17 5.067159E−15 −1.442430E−16  1.303177E−17  5.222514E−17 C4  2.771063E−20−2.297083E−19 −4.973879E−20  4.998372E−22 −4.373272E−21 C5 −3.914426E−24 4.468892E−23  1.037858E−23  2.854081E−26  2.022375E−25 C6  2.025798E−28 6.699558E−27 −7.916827E−28 −4.246522E−30 −5.622426E−30 Face 30 = 40 36= 34 48 52 63 K  0  0  0  0  0 C1  7.462841E−08 −6.215300E−08−1.263170E−07 −3.644419E−08  1.073460E−07 C2 −1.480049E−12  3.990211E−12 1.704645E−12  2.830363E−12  3.012743E−11 C3  7.038597E−18 −2.682924E−16−1.072376E−16 −6.930387E−17 −1.142275E−15 C4 −6.746798E−21  1.575407E−20 1.095795E−19 −7.697280E−21  2.057679E−19 C5  1.842201E−24 −6.565311E−25−9.786894E−24  7.864096E−25  1.754484E−23 C6 −1.185318E−28  1.800037E−29 8.828862E−28 −2.506008E−29  3.450730E−27

1. (canceled)
 2. A projection objective for projecting a mask patternarranged in an object plane of the projection objective into an imageplane of the projection objective, the projection objective comprising:a first concave mirror arranged in the vicinity of a first pupil planeof the projection objective; a second concave mirror arranged in thevicinity of a second pupil plane of the projection objective; a firstfolding mirror that reflects light from the object plane toward thefirst concave mirror; a second folding mirror that reflects light fromthe second concave mirror toward the image plane; and a lens arrangedbetween the second folding mirror and the image plane.
 3. The projectionobjective of claim 2, wherein the lens is one of a plurality of lensesarranged between the second folding mirror and the image plane.
 4. Theprojection objective of claim 2, further comprising: a third foldingmirror that reflects light from the first concave mirror; and a fourthfolding mirror that reflects light from the third folding mirror towardthe second concave mirror.
 5. The projection objective of claim 2,wherein the projection objective has a magnification not equal to one.6. The projection objective of claim 2, wherein an odd number ofintermediate images are formed in the projection objective.
 7. Theprojection objective of claim 6, wherein exactly three intermediateimages are formed in the projection objective.
 8. The projectionobjective of claim 6, wherein a sum of the number of intermediate imagesand a number of mirrors in the projection objective is an odd wholenumber.
 9. The projection objective of claim 2, further comprising afirst negative lens that is arranged in front of the first concavemirror at a distance therefrom.
 10. The projection objective of claim 9,wherein no optical element is arranged between the first negative lensand the first concave mirror.
 11. The projection objective of claim 9,further comprising a second negative lens that is arranged in front ofthe second concave mirror at a distance therefrom.
 12. The projectionobjective of claim 11, wherein no optical element is arranged betweenthe second negative lens and the second concave mirror.
 13. Theprojection objective of claim 2, wherein the image plane is arranged atan element for a liquid crystal display.
 14. A projection objective forprojecting a mask pattern arranged in an object plane of the projectionobjective into an image plane of the projection objective, theprojection objective comprising: a first concave mirror arranged in thevicinity of a first pupil plane of the projection objective; a secondconcave mirror arranged in the vicinity of a second pupil plane of theprojection objective; a first folding mirror that reflects light fromthe object plane toward the first concave mirror; a second foldingmirror that reflects light from the second concave mirror toward theimage plane; and a lens arranged between the object plane and the firstfolding mirror.
 15. The projection objective of claim 14, wherein thelens is one of a plurality of lenses arranged between the object planeand the first folding mirror.
 16. A projection objective for projectinga mask pattern arranged in an object plane of the projection objectiveinto an image plane of the projection objective, the projectionobjective comprising: a first concave mirror arranged in the vicinity ofa first pupil plane of the projection objective; a second concave mirrorarranged in the vicinity of a second pupil plane of the projectionobjective; a first folding mirror that reflects light from the objectplane toward the first concave mirror; and a second folding mirror thatreflects light from the second concave mirror toward the image plane;wherein an image-side numerical aperture of the projection objective isgreater than 0.7.
 17. The projection objective of claim 16, wherein theimage-side numerical aperture of the projection objective is not lessthan 1.0.